| 摘要 |
PROBLEM TO BE SOLVED: To obtain L-aspartic acid in good efficiency, in high purity and in high yield by reacting maleic acid with ammonia in the presence of a modified maleic acid isomerase having good oxidation stability, or the like. SOLUTION: This method for producing L-aspartic acid comprises enzymatically reacting maleic acid with ammonia in the presence of the cultured product (treated product) of a microorganism producing maleic acid isomerase and the cultured product (treated product) of a microorganism producing aspartase. Therein, the maleic acid isomerase is the one having an activity deterioration rate of <40%, when a cell-free extract solution of the crushed cell product of Escherichia coli JM109 transformed with a DNA encoding the maleic acid isomerase is oxidized with 30 mM hydrogen peroxide at 30 deg.C for 1 hr. The maleic acid isomerase is obtained by replacing the 201-methionine residue of the amino acid sequence of the formula by an amino acid residue, such as cysteine residue, having more stability against oxidizing treatments than that of the methionine residue. |
